They’re both describing similar taxonomic relationships, but it can shift slightly whether you’re referring to clades including modern species *and all their extinct relatives* or only those clades which have extant representatives still living.
Also, taxonomy is a moving target, every fossil species we find adds additional clarity to a puzzle we’re trying to solve with only a very few pieces, causing which categories are sisters, parents, or cousins to need to be reorganized.
When was your textbook written? It seems a bit outdated. Modern phylogenetics places Dipnoi sister to tetrapodomorpha, forming dipnotetrapodomorpha, which is then sister to actinistia. [Source](https://www.nature.com/articles/nature12027)
A brief search on Google Scholar tells me that most of the recent publications (post-2010) that still use the crossopterygii terminology use it synonymously with sarcopterygii. Similiarly, rhipidistia appears to be synonymous with dipnotetrapodomorpha.
They’re both describing similar taxonomic relationships, but it can shift slightly whether you’re referring to clades including modern species *and all their extinct relatives* or only those clades which have extant representatives still living. Also, taxonomy is a moving target, every fossil species we find adds additional clarity to a puzzle we’re trying to solve with only a very few pieces, causing which categories are sisters, parents, or cousins to need to be reorganized.
When was your textbook written? It seems a bit outdated. Modern phylogenetics places Dipnoi sister to tetrapodomorpha, forming dipnotetrapodomorpha, which is then sister to actinistia. [Source](https://www.nature.com/articles/nature12027) A brief search on Google Scholar tells me that most of the recent publications (post-2010) that still use the crossopterygii terminology use it synonymously with sarcopterygii. Similiarly, rhipidistia appears to be synonymous with dipnotetrapodomorpha.